A couple subneting questions

[Ipsec Espah]

I'm doing some practice problems and theres a couple i'm not to sure about.

1. Which one of the following does not belong to the same subnet as the other three when using 255.255.224.0 as the subnet mask?

a. 172.16.66.24
b. 172.16.65.33
c. 172.16.64.42
d. 172.16.63.51

2. You are designing an IP addressing scheme for a large network with 4 subnets. You expect to add a subnet each year for the next 4 years? The network ID is 10.1.1.0. What subnet mask should you assign to allow for the maximum amount of hosts per subnet?

a. 255.0.0.0
b. 255.254.0.0
c. 255.240.0.0
d. 255.255.255.0

Any help is appriciated.

[MrLinus]

1. Which one of the following does not belong to the same subnet as the other three when using 255.255.224.0 as the subnet mask?

a. 172.16.66.24
b. 172.16.65.33
c. 172.16.64.42
d. 172.16.63.51

d -- Basically, 224 takes the following binary:

128 64 32 16   8 4 2 1
1   1   1  0    0 0 0 0

The bolded area represents the network. The first viable network range goes from 32.1 to 63.254, then 64.1 to 95.254. The first three are in the same subnet. The last is in the previous subnet.

2. You are designing an IP addressing scheme for a large network with 4 subnets. You expect to add a subnet each year for the next 4 years? The network ID is 10.1.1.0. What subnet mask should you assign to allow for the maximum amount of hosts per subnet?

a. 255.0.0.0
b. 255.254.0.0
c. 255.240.0.0
d. 255.255.255.0

Hrmm. The closest would be d in my opinion. Although I'd say it's an oddly worded question. Basically, I worked it out based on the humber of subnets required -- 8. That means I need 8 binary values turned on for the subnet mask. We flip our binary numbers around. Normal in subnetting we count from largest to smallest but instead we'll do the traditional of smallest to largest:

1 2 4 8 16 , etc.

This means I need at least the first four (4) bits turned on, which equals 240 (128+64+32+16), which would normally make me choose c. But since the network ID takes 2 extra places as it is, I'd have to go with d.

Make sense? You might want to check out the tutorials on subnetting here at AO in the Tutorials section.

[Ipsec Espah]

Woot! Thank you! I just got back from taking the teachers Cisco semester 1 exam and if i missed one it would be a carless mistake... I got a 100 on Cisco's exam so getting a 100 on the teachers wouldn't be to bad Thanks for your help